The most usual way of monitoring EKG is a so-called 3-wire connection. In some cases, however, e.g. when cardiac ischemia is suspected, it is desireable to use a 5-wire measuring connection. On the other hand, the EEG-monitoring especially during a surgical operation has been found a good measuring variable, which correlates with the depth of anaesthesia and warns the brain of a threatening lack of oxygen. However, the EEG-monitoring has been generally considered troublesome; partly due to difficulties encountered in the interpretation of EEG but partly also due to the complexity, high price and bulkiness of an EEG-apparatus and the extra trouble caused by electrode connections.